1. Field of the Invention
The present invention relates to photopolymerizable compositions and particularly to photopolymerizable compositions containing a photopolymerization initiator having a novel composition which are sensitive to, for example, argon laser rays.
2. Description of the Prior Art
Hitherto, it has been well known to form images by a process which comprises preparing a photopolymerizable composition comprising an addition-polymerizable compound having at least one ethylenically unsaturated double bond (hereinafter "ethylenic compound"), a photopolymerization initiator and, if necessary, an organic high molecular substance having film-forming ability, a thermal polymerization inhibitor or a plasticizer, etc., producing a solution of this photopolymerizable composition, applying the solution to a base to produce a photosensitive material providing with a photopolymerizable composition layer (photosensitive layer), exposing imagewise to light the photosensitive layer using a desired original, polymerizing the exposed area to harden it and treating with an organic solvent capable of dissolving the nonhardened area to remove the nonhardened area by dissolution, by which an image composed of the hardened area is formed. Alternatively, images have been formed by a process which comprises producing a laminate by pressing to adhere the above-described photosensitive material to another image supporting base (either the base of the photosensitive material or the image supporting base is transparent), exposing imagewise to light at the transparent base side, polymerizing the exposed area of the photosensitive layer to vary the adhesive strength of the photosensitive material to the base and that of the photosensitive material to the image supporting base such that the degree of adhesion is different between the exposed and unexposed areas and separating both bases, by which the photosensitive layer in the unexposed area transfers to one base and the photosensitive layer in the exposed area adheres to other base to form an image composed of the photosensitive layer respectively. In such processes, benzyl, benzoin, anthraquinone or Michler's ketone, etc., have been used as a photopolymerization initiator. However, the photopolymerizable compositions containing these photopolymerization initiators have a problem that they are hardly sensitive to ultraviolet rays of a long wavelength or visible rays such as argon laser, etc., and do not exhibit polymerization initiating ability, though they are sensitive to ultraviolet rays having a comparatively short wavelength. It is very desirable to use visible rays or a light source capable of scan exposure, for example, laser rays as a light source for exposure in image formation.